1. Field of the Invention
The present invention relates to an adhesive film for semiconductor, a lead frame and a semiconductor device using the same.
2. Description of the Related Art
In recent years, large-sized semiconductor chips are increasingly manufactured for mass storage and high performance. In contrast, packages for such semiconductor chips are required to be small-sized in view of limitations for print circuit designs, and demand for miniaturized electronic devices. Correspondingly, some new mounting modes have been proposed to deal with the densification and the high density mounting of semiconductor chips. One mounting mode is a lead on chip (LOC) mode for memory devices in which leads are adhered onto the chips. The LOC mode enables rationalization of in-chip wiring and wire bonding, high speed signal transmission by wiring compaction, and a small-sized package.
In such a new mode, there is provided an adhesion interface between the semiconductor chip and the lead frame, which are composed of different materials. Its adhesion reliability largely affects the reliability of a semiconductor package. Also significantly, a wire connecting the semiconductor chip and the lead frame should not be broken in a temperature cycle test (heat cycle test) which is one of indices for the semiconductor package reliability, as well as thermal durability during package assembling processes, and adhesion workability.
For such adhesion, a paste adhesive, or an adhesive applied to a heat-resistant substrate has been conventionally used. One example is a hot-melt type adhesive film using a polyimide resin. See Japanese Unexamined Patent Application Publication Nos. 5-105850, 5-112760, and 5-112761. The hot melt type adhesive has high glass transition temperature, and therefore adheres to an adherend only at very high temperature. The adherend such as high density semiconductor chips and copper lead frames is likely to be thermally damaged.
In order to provide an excellent semiconductor package temperature cycle property, the adhesive film needs to have a reduced coefficient of linear expansion close to that of the semiconductor chip and the lead frame, and a decreased storage elastic modulus for relaxing stress induced by the temperature cycle. However, if the storage elastic modulus is too small, the semiconductor chip cannot be connected to the lead frame upon wire bonding in the semiconductor package manufacturing steps.
As semiconductors have become more integrated, the material for the lead frame has changed from 42 alloy to copper for high-speed signal processing. Further, a low temperature adhesion property and a temperature cycle property are also needed to prevent oxidation of copper due to heat upon the tape and the chip adhesion, and to relax thermal stress due to a difference between the thermal expansion coefficient of the copper and that of the chip.
Accordingly, it is an object of the present invention to provide an adhesion film for semiconductor that allows a semiconductor element to adhere to a lead frame at low temperatures with an excellent temperature cycle property.
Another object is to provide a lead frame with an adhesive film that can adhere to a semiconductor element at low temperatures, and can provide a highly reliable semiconductor device.
Still another object is to provide a highly reliable semiconductor device adhered with an adhesive film that adheres at low temperatures and provides an excellent temperature cycle property.
The present inventors have been engaged in the development of an adhesive film for semiconductor having both a low temperature adhesive property and an excellent temperature cycle property. As a result, it has been found that the above-mentioned problems can be solved by using an adhesive having specific properties, and by limiting the total thickness of an adhesive film including a support film and the adhesive layers on both sides of the support film.
A first aspect of the present invention provides an adhesive film for semiconductor, comprising: a support film; and adhesive layers formed on both surfaces of the support film, in which each adhesive layer comprises an adhesive having a glass transition temperature of 200xc2x0 C. or less, a coefficient of linear expansion of 70 ppm or less, and a storage elastic modulus of 3 GPa or less, and the adhesive film has a total thickness of between 43 and 57 xcexcm.
A second aspect of the present invention provides a lead frame with an adhesive film for semiconductor, comprising: a lead frame, and the aforementioned adhesive film for semiconductor according to the present invention adhered to the lead frame.
A third aspect of the present invention provides a semiconductor device, comprising a lead frame and a semiconductor element, in which the lead frame and the semiconductor element are adhered to each other by means of the aforementioned adhesive film for semiconductor according to the present invention.